Vacuum pump apparatus



May 3, 1966 w. A. LLOYD ETAL 3,249,290

VACUUM PUMP APPARATUS United States Patent 3,249,290 VACUUM PUMP APPARATUS William A. Lloyd, San Jose, and William R. Wheeler, Saratoga, Calif., and Renn Zaphiropoulos, Torino, Italy, assignors to Varian Associates, Palo Alto, Calif.,

a corporation of California Filed Mar. 10, 1964, Ser. No. 350,848 8 Claims. (Cl. 230-69) This invention relates in general to vacuum pump apparatus, and more particularly to vacuum pump apparatus employing both magnetically confined -glow discharge and sublimation pumping. Such pump apparatus are extremelyuseful in providing uncontaminated high vacuum and a large Working space, as required in, for examplc, thin film deposition, high altitude simulation, friction studies and semiconductor processing.

Vacuum pumps such as disclosed and claimed in U.S.

Patent 2,993,638, dated July 25, 1961 and assigned to the same assignee as the present invention have been built which employ a magnetically coniined glow discharge established between .energized anode and cathode members contained within the pump envelope to reduce the pressure therein and thereby reduce the pressure within a system to which the pump envelope is connected.

Commercially feasible prior art magnetically confined glow discharge pumps have usually taken on one of three forms. In the -irst of these an envelope surrounds and is closely spaced from the pumping elements, and magnetic means are disposed about the envelope. The pumping elements usually comprise a cellular anode disposed bet'ween a pair of planar cathode members, or a plurality of these anode members interleaved with a plurality of cathode members suspended within the pump envelope. The pum-ping speed 'of this Ifirst type is often less than desired since access from the structure being evacuated to the pump envelope which is normally through a conduit or throat having a diameter less than the characteristic transverse `dimension of the pump envelope or the structure being evacuated, is limited to only a portion of the pump element or elements. Also, gap length of the magnets is fairly substantial thereby serving to increase the size of the solenoid or the permanent magnets as the case may be. v

In the second type the pump is provided with a large central chamber and a plurality of lesser chambers extending outwardly therefrom like the spokes of a wheel in each of which pumping elements are disposed. Permanet magnet means are carried externally of the pump envelope and between the spoke-like outward protrusions. In this second type of pump speed is again limited since access is only provided to one side of each pumping element. Also, the envelope for this type of pump is difcult and expensive to fabricate.

In the third type of commercially feasible pump a single pumping element is vertically disposed and centrally positioned within an elongated central pumping chamber #which communicates 'with a pair of gas access chambers on opposite sides of the central chamber. With this type of pump, while gas access is somewhat increased, magnetic gap length is quite substantial so that large permanent magnets must be used. A plurality of pumping elements could actually be stacked vertically so as to increase pumping speed but this would further increase gap length and the resulting scaled up pump would be awkward to use.

Pumping bythermally evaporating or subliming reactive metals froma heated filament onto the walls of a pump housing has been well known for many years.

' Gas molecules coming in contact therewith combine chemically or physically with the condensed material and 3,249,290 Patented May 3, 1966 ICC.

are removed from the gaseous state so as to reduce the pressure. Pumping by means of sublimation alone has proven in practice to have extremely high pumping speeds (in excess of 3500 liters/ sec.) for the active gases such as O2, N2, CO and CO2, but suffers from the inability to pump inactive gases, such as the noble gases. However, in combination with a magnetically confined glow discharge pump a most practical and useful vacuum pump apparatus results.

Accordingly, it is the principal object of this invention to provide a vacuum pump apparat-us employing both magnetically confined glow discharge and sublimation pumping which has greatly enhanced pumping speed and which is compact and easy to fabricate, use and service.

' One feature of the present vinvention is the provision of a symmetrical combination magnetically confined glow discharge and sublimation vacuum pump having an envelope with thin rectangular channels passing therethrough for accommodating permanent magnets.

Another feature of the 'present invention is the provision of a pump of the above type wherein the channels are made of a reactive material and'thereby serve the dual function of isolating the magnets from the vacuum system and of acting as the cathodes of the magnetically confined glow discharge device.

Still another feature of the present invention is the provision of a vacuum pump apparatus, a system to be evacuated and means for connecting the pump apparatus to the system to be evacuated wherein the characteristic transverse dimension of the apparatus, system and connecting means are substantially equal.

These and other objects and features of the presentl invention and a further understanding may be had by referring to the following description and claims, taken in conjunction with the following drawing in which:

FIG. 1 is a front view partially broken away of the novel vacuum pump apparatus of the present invention;

FIG. 2 is an enlarged cross-sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along the lines 3--3 of FIG. 1;

FIG. 4 is an enlarged cross-sectional view of the area delineated by the lines 4--4 of FIG. 2;

FIG. 5 is an alternate embodiment showing pumping elements utilized in the .present invention; and

IFIG. 6 is a graph of pressure vs. time for a typical operating cycle of the present invention.

Referring now to FIG. 1 there is shown a vacuum pump apparatus 11 incorporating the novel features of the present invention. The apparatus 1.1 comprises generally a chamber 12 to be evacuated removably sealed to a sump 113 containing therein the combination high vacuum pumping system to be explained in more detail below. Rough pumping of the chamber 12 and sump 13 is accomplished in a contaminant-free fashion by sequential operation of refrigerated sorption pumps 14. Efcient bakeout is effected by means of strip-type heaters 15 mounted directly to the outer walls of the chamber 12 and sump 13. Shrouds 16, 17 and 18 cover the chamber 12 and sump 413 so as to protect operating personnel from danger during bakeout and aid in providing a uniform temperature over the surface of the chamber 12 and sump 13. A blower 19 cools the sump 13 and chamber 12 immediately upon completion of bakeout. Power supplies (not shown) for the apparatus 11 may be compactly mounted in a cabinet 20 disposed adjacent the chamber 12 and sump 13. A powered hoist 21 controlled by hand or foot allows easy lifting of the chamber 12 when the apparatus is to be opened 3 to air. The entire apparatus may be seated on a platform 22. i

The chamber 12 may consist of a cylindrical bell jar made of, for example, 304 stainless steel 1A thick and provided with viewing ports 23 located in the walls of the bell jar and which extend outwardly through openings in the shroud 16. In one embodiment the bell jar is 18 in diameter and 30 high. The base of the bell jar is secured in vacuum tight manner by, for example, welding to a large diameter, all metal high vacuum sealing flange 24 for example, the kind shown and disclosed in U.S. patent application Serial No. 256,744, tiled February 6, 1963 and assigned to the same assignee as the present invention.

Referring now to FIGS. 1-4 the sump 13, cylindrical in shape and made of, for example, 304 stainless steel 1A thick, has a series of vertically spaced rectangular openings positioned on opposite sides. These openings are adapted to receive a plurality of longitudinally extending, non-magnetic, gas impervious channels 25 rectangular in cross-section which pass through the sump 13 and are sealed in vacuum tight manner to the outer walls of the sump 13 at 26 by, for example, heliarc welding. In one embodiment the sump 13 is 18 in diameter and 361/2 long. The channels 25 are made of 304 stainless steel Ms" thick and are spaced 111/16" from each other. Three middle channels are 3l x 5 in cross-section, the top channel x 5 and the bottom channel 4" X 5.

Each of the channels are adapted to receive a permanent magnet 27, for example, a ferrite magnet which runs longitudinally of the channels 25. The magnets 27 are in intimate contact with the horizontal walls of the channels 25 and are spaced from the vertical walls of the channels 25 so as to provide coolant passages running through the channels 25 on opposite sides of the magnets 27. If desired, and as shown in the drawing, the uppermost and bottom-most channels might actually contain two permanent magnets 27, 28 with the magnets 28 heing connected to magnets external of the channels 25 having portions 29 running normal to the longitudinal direction of the permanent magnets 27. The portions 29 provide a return path for the magnetic field of the magnets 28 and increase average magnetic field intensity.

A horizontal magnet stop 30 welded across the face of each channel 25 at one end and a single vertical removable clamping bar 31 disposed across the faces of each of the channels 25 at their opposite end serve to retain the permanent magnets 27 in place.

Referring more particularly to FIGS. 2-4 a plurality of replaceable pumping element canisters 32 of the type disclosed in U.S. Patent 2,983,433 issued May 9, 1961 are interleaved with the channels 25 and include a pair of spaced apart reactive cathode members 33, each member 33 being in intimate contact with .the walls of the channels 25, and a cellular anode member 34 disposed between and insulated from the pair of cathode members 33. Tabs 35 Welded to the top and `bottom channels 25 are adapted to receive a vertical retaining rod 36 which holds the pumping element canisters in place. The use of the canisters 32 facilitates replacement. A high positive voltage is applied to the anode members 34 with respect to the cathode members 33, via the intermediary of a high voltage feedthrough 37 passing through the Wall of the sump 13, a strap 3S and leads 39. The permanent magnets 27 and the pumping element canisters 32 make up the magnetically confined glow discharge portion of the high vacuum pump apparatus of the present invention, the magnetic lines of force ybeing substantially parallel to the anode cell axes and perpendicular to the cathodes.

Referring to FIG. 2 a replaceable sublimation pump or cartridge 40 is adapted to be inserted in vacuum tight fashion by means of high vacuum fittings 41 through an opening in the side wall of `the sump 13. The type of p the cartridge `40 and platform 42 in such a manner as v to shield the workpieces from the subliming material but not to impede the owof gases from the chamber 12 to the sump 13. Of course, additional sublimation pumps may vbe used to make the system suitable for long term, e.g., 10,000 hours, environmental testing.

The neck of the sump 13 is provided with a plurality of feedthrough ports which are adapted to accept standard feedthroughs, for example, high voltage feedthrough 44,

high current feedthrough 45;` Those not in use'are covered in vacuum tight fashion, as at 46, 47.

The lip of the sump 13 is secured in vacuum tight manner by, for example, Welding to a large diameter, all metal high vacuum sealing flange Z4. A copper wire gasket 48 is positioned lbetween the opposing faces of the flanges 24 and 24. Up'on tightening of the clamp 49 the copper wire gasket 48 is compressed thereby forming a Vacuum tight seal between the opposing anges 24, 24 and joining the chamber 12 and sump 13 in vacuum tight A communication.

The roughing system produces a completely contaminant free roughing vacuum and includes a roughing manifold 50 connected in vacuum tight communication to au exhaust conduit 51 leading into the sump 13. A plurality (3) of sorption pumps 14 which may be chilled by liquid nitrogen (not shown) held in dewars 52 are each connected through a high vacuum tting and to a high vacuum valve 53.l An additional all metal high vacuum valve 54 isolates the manifold 50 from the sump 13. The manifold is isolated from the atmosphere at 55. Asingle, mechanical pump could ybe used in the roughing system instead of refrigerated sorption pumps.

In operation, to be explained with reference to the graph of FIG. 6 and with the bell jar 12 and shroud 16 raised by the powered hoist 21, workpieces are placed upon the platform 42. The bell jar 12 and shroud 16 are then lowered and the clamps 49` tightened so as to join the bell jar 12 and sump 13 in vacuum tight communication.

With the valves 53 and 54fcloscd the dewars 52 are lled with liquid nitrogen. Then valve 54iis opened and `each of the valves 53 are sequentially opened and the pumps 14 sequentially operate in the manner described in U.S. application Serial No. 110,425, filed May 16, 1961, now U.S. Patent 3,172,748 issued March 9, 1965, and assigned to the same assignee as the present invention. This reduces the pressure within the bell jar 12 and sump 13 to on the order of 106 torr and corresponds to the portion of the curve designated A in FIG. 6.

The titanium pump 40 and anode 34 are energized from control units (not shown) and with the shroud 17in place the heaters 15 are activated so as to bakeout the entire system. In a typical operating cycle the bell jar 12 is baked out to a temperature of 250 C., and sump 13 is baked to a temperature of 200 C. Thisvcorresponds to the portion of curve designated B in FIG. 6. Immediately upon completion of the bakeout the blower 19 is turned on and forces cooling air into theshroud 418 which is deflected by baies 56 so as to circulateiair through the channels 25,then up through shroud 17 and 16 and out to the surrounding atmosphere. This corresponds to the point C` in the graph off FIG. 6. Using both magnetically confined glow discharge and sublimation pumping, pressures on the order of 10-10 torr and even lower can be obtained. This corresponds to the portion of the curve designated D in FIG. 6.

Referring now'to FIG. 5 there is shown an alternate embodiment of the magnetically coniined glow discharge pumping structure ,wherein the channels 25 .are `made of a reactive material so th-at they may serve as the cathodes. Thus, spacing between channels 25 may be reduced to thereby reduce the air gap between the opposing permanent magnets 27 so that the same magnets can be used more eiciently or smaller magnets may also be used. In addition, channels 25 may be made removable to facilitate replacement when they-become Worn.

The above describes a single symmetrical compact apparatus which is relatively easy to fabricate. Moreover, by making the bell jar 12, connecting means 24, 24', 48 and sump 13 all the same diameter the pumping elements are easily accessible when the apparatus is open and not in operation, while during 'operation the sump and connecting means yoffer minimum impedance to the ow of gases into the pump, thereby enhancing pumping speed.

The design also permits placement of the magnets as close as possible to the anode-cathode members and Without having to place the magnets directly within the sump, While at the same time avoiding the necessity of fabricating complex envelope structures ordinarily required f to accommodate external magnets.

In certain applications where high dissipation pumps are utilized the channels 25 could be used for circulating a refrigerant therethrough so as to cool the pumping elements further.

Since many changes can be made in the above construction and many apparently widely diierent embodiments could be made without departing `from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limitv ing sense.

' members so as to enhance said glow discharge, said magnetic means being disposed within said channels passing through said envelope.

2. The apparatus according to claim 1 including means for circulating a coolant fluid through said channels.

3. The apparatus according to claim 1 including means for evaporating a source of active material Within said envelope.

4. The apparatus according to claim 1 wherein said envelope, structure and connecting means have substantially the same transverse dimension.

5. A high vacuum pump apparatus comprising: Ia gas impervious, non-magnetic envelope adapted to be connected to a structure it is desired to evacuate; aplurality of gas impervious, non-magnetic, spaced-apart channels made of a reactive metal passing through said envelope; a plurality of anode members disposed within said envelope and being interleaved with said channels, said anode members and said channels being adapted t0 initiate and maintain a glow discharge upon energization thereof; and, means for producing and directing a magnetic field through said anode members and said channels so as to enhance said glow discharge, said magnetic means being disposed within said channels passing through said envelope.

6. The apparatus according to claim 5 including means for circulating a coolant fluid through said channels.

7. The apparatus according to claim 5 including means for evaporating a source of reactive material within said envelope.

8. The apparatus according to claim 7 wherein said envelope, structure and connecting means have substantially the same transverse dimension.

References Cited by the Examiner UNITED STATES PATENTS 2,983,433 5/1961 Lloyd et al. 230-69 2,993,638 7/1961 Hall et al 230-69 3,112,864 12/1963 Hall et al. 230--69 3,117,247 l/l964 Jepsen 230-69 X MARK NEWMAN, Primary Examiner.

DONLEY J. STOCKING, Examiner. 

1. A HIGH VACUUM PUMP APPARATUS COMPRISING: A GAS IMPERVIOUS, NON-MAGNETIC ENVELOPE ADAPTED TO BE CONNECTED TO A STRUCTURE IT IS DESIRED TO AVACUATE; A PLURALITY OF GAS IMPERVIOUS, NON- MAGNETIC, SPACED APART CANNELS PASSING THROUGH SAID ENVELOPE; A PLURALITY OF PUMPING ELEMENTS DISPOSED WITHIN SAID ENVELOPE AND BEING INTERLEAVED WITH SAID CHANNELS, SAID PUMPING ELEMENTS INCLUDING AN ANODE MEMBER AND A CATHODE MEMBER SPACED FROM SAID ANODE MEMBER, SAID ANODE AND CATHODE MEMBERS ADAPTED TO INITIATE AND MAINTAIN A GLOW DISCHARGE UPON ENERGIZATION THEREOF; AND, MEANS FOR PRODUCING AND DIRECTING A MANGNETIC FIELD THROUGH SAID ANODE AND CATHODE MEMBERS SO AS TO ENHANCE SAID GLOW DISCHARGE, SAID MAGNETIC MEANS BEING DISPOSED WITHIN SAID CHANNELS PASSING THROUGH SAID ENVELOPE. 